This research is designed to extend our studies of the effects of overnutrition and undernutrition on thyroid hormone physiology and to separate those effects which are related to the caloric balance or composition of the diet from those which are associated with change in body weight or body composition. Studies will be performed in normal and obese volunteers, patients with anorexia nervosa and lipoatrophic diabetes and in normal, hypothyroid, protein malnourished and congenitally obese Zucker rats. Measurements of serum concentrations and kinetics of thyroxine, triiodothyronine, reverse triiodothyronine and of the pituitary response of thyroid stimulating hormone to thyroid releasing hormone will be correlated with changes in thermogenesis, thyroid sensitive enzymes, and body composition.